refactor/fix: css organization and error rendering (#3117)

* fix: php notice

* refactor/feat: merge HtmlFormat.css into style.css

Also improve ux of error rendering.

* fix: center-align footer text

bridges/FeedMergeBridge.php

@@ -59,6 +59,7 @@ TEXT;
 
         foreach ($feeds as $feed) {
             // Fetch all items from the feed
+            // todo: consider wrapping this in a try..catch to not let a single feed break the entire bridge?
             $this->collectExpandableDatas($feed);
         }